To assist in this task, it is known to use computer-aided tools for generating a target land contour for a worksite, based on surveying data of the original contour of the land in question. These tools generate models from which elementary tasks can be e.g. assigned to various items of on-site apparatus, such as earthmoving-apparatus, the latter in some cases being automated to varying degrees. The earthmoving apparatus or its operator needs to be provided at all times with all the necessary information for conducting the task at hand at its location. This information will generally have various possible sources: a central model held at an on-site office, external devices such as beacons, laser guides, onboard sensors, and the like. As the tasks to be performed by an earthmoving apparatus are inextricably linked to its exact physical location, it has become usual practice to provide each item of mobile apparatus with a positioning device such as a GPS receiver and two-way communication links with different stations, or possibly other mobile apparatus on the site.
In this connection, patent document U.S. Pat. No. 5,631,658 discloses a system for automatically operating geography-altering machinery in a worksite on the basis of a pre-established three-dimensional model of the target contour relative to an existing contour. The latter is divided into elementary grid elements which can be indexed with the position of a contour-modifying tool of a particular earthmoving apparatus. A computerised system on board of the earthmoving apparatus stores the site plan, identifies the current position and elevation of the contour-modifying tool using a GPS device, and automatically determines the actions to be performed with that tool to make the existing contour at that local level correspond to the target contour.
In the field of open-cast mining, patent document U.S. Pat. No. 5,850,341 discloses a system for monitoring the removal of ore with reference to a three-dimensional map of the mine. The map is subdivided into elementary regions which are differentiated according to the type or grade of ore they contain, that information being acquired and recorded at an initial phase. The mobile excavating machinery is provided with a GPS receiver for positioning relative to the map and a sensor for detecting the amounts of ore removed. This information is correlated with the data concerning the ore to control the mobile excavating operations and keep track of the excavated ore.
Patent document U.S. Pat. No. 5,935,192 discloses a database technique for identifying and associating information with elementary sections of a worksite. Each section of the worksite is defined by a corresponding data object occupying two dimensions of a layered data organisation. The layers are classed as objects, each associated with a parameter of the worksite. The information is used notably for a differencing algorithm to direct the operations of working machines through an operator display or an automatic controller.
Patent document U.S. Pat. No. 5,404,661 discloses a technique for acquiring the three-dimensional position coordinates of a work tool in relation to a stored model of a worksite. The tool position information is obtained through a GPS in cooperation with a dynamically updatable database.
Patent document U.S. Pat. No. 6,463,374 discloses a technique for guiding agricultural vehicles, especially for obtaining appropriate spraying patterns over areas of complex contours.